In Baghdad this week, a military tribunal is deciding whether five American soldiers must stand trial for the rape and murder of an Iraqi girl and the killing of her parents and sister in March.

The alleged events, which are among several atrocities tied to US forces now in their fourth year of fighting insurgents in Iraq, raise important questions for military officials: How do the numbers and types of incidents compare with earlier wars? Is there something about this conflict that makes such incidents more likely? Could they have been anticipated and prevented?

It's hard to compare Iraq with previous wars because the fighting and the reasons for fighting are different as are the numbers and deployment of troops. But observers generally agree that charges involving mistreatment of civilians or enemy combatants are not disproportionate compared with World War II, the Vietnam war, or other wars.

"You could probably construct an empiri-cal case that US forces are exhibiting more restraint in their treatment of Iraqi civilians than has ever been seen in past wars of similar scale and duration," says military analyst Loren Thompson of the Lexington Institute in Arlington, Va, in an e-mail. "Almost all of the atrocities that have been alleged involve small units deliberately disobeying rules of engagement and the orders of senior officers."

"It is worth bearing in mind that the US routinely killed thousands of enemy civilians in bombing raids during World War II, and that the number of civilians murdered at My Lai, the worst atrocity committed by US forces in Vietnam, was over 300," adds Dr. Thompson. "The pattern of atrocities committed against civilians in past counterinsurgency campaigns is quite imposing, from the British Army in the Boer War to the US Army in the Filipino Insurrection to the Russian Army in Chechnya."

For example, the Los Angeles Times published over the weekend details of a 9,000-page once-secret archive, assembled by a Pentagon task force in the early 1970s, showing that "confirmed atrocities by US forces in Vietnam were more extensive than was previously known."

Similarly, it's likely to be years before the full extent of such events in the Iraq war is known.

Beyond this week's military hearing in Baghdad, investigators are looking into:

•An episode involving US marines and 24 civilians killed at Haditha in November. It's expected to result in official charges involving failure by some officers to report the event as well as the deaths of the Iraqis.

•Charges against six marines for assaulting civilians in order to extract intelligence. Among the six are three charged with killing an Iraqi man, then placing an AK-47 rifle next to his body to make it look as if he was an insurgent.

•Allegations that an Army brigade commander in Tikrit ordered his troops to "kill all military-aged males."

What's different, compared with World War II – at least for American soldiers in the field – is the incessant nature of the threat of personal attack from roadside bombs or snipers.

"Criminal behavior is a symptom of combat stress," says John Pike, director of GlobalSecurity.org. "For troops who go outside the wire, as opposed to fobbits [those who remain inside forward operating bases or FOBs], they would be exposed to combat stressors on a daily basis for most of their tour. During previous wars, the probability of dying in combat was higher. But for most soldiers, combat was episodic, rather than continuous."

At the same time, history has shown, counterinsurgency campaigns increase the likelihood that troops may mistreat civilians, because small units spend long periods surrounded by local people whose language and customs they don't understand. Things become even more difficult as a country moves toward civil war.

"Constantly harassed, constantly on guard, not sure who is with us or against us or simply passive, IEDs randomly striking convoys at places that were clear the day before, sectarian strife bordering on civil war, and a political system that seems incapable of getting its act together are some of the factors creating the psychology of lawlessness in which atrocities occur," says Dan Smith, a retired Army colonel who served in Vietnam as an infantry platoon leader and intelligence adviser and is now affiliated with the Friends Committee on National Legislation, the Quaker lobby in Washington.

Other military analysts point to a confluence of trends as the war goes on: the Army's need at times to recruit more soldiers from the lowest acceptable category, extended and multiple tours, and no longer being welcomed by Iraqis.

"The problem is, we're now asking our troops to do something they weren't trained to do," says Charles Peña, a defense consultant and policy scholar at the Coalition for a Realistic Foreign Policy, a Washington think tank. "The population they feel they were sent to save no longer feels grateful to have been saved."

Some observers note another trend indicating a breakdown in discipline.

"What I see as unusual in Iraq is the number of cases in which officers and noncommissioned officers have been involved, not only indirectly but directly," says Gary Solis, a former judge in the Marine Corps who taught military law at West Point and now teaches at Georgetown University Law Center. "Warrant officers, lieutenants, captains, lieutenant colonels and, now, even a colonel have fallen under suspicion."

A recent Associated Press roundup of criminal cases against US servicemen stemming from deaths of Iraqis includes a major, three captains, a 1st lieutenant, a chief warrant officer, a sergeant 1st class, four staff sergeants, and three sergeants.

While the number and type of alleged atrocities may be troubling, the military response appears to have been deliberate and open. "If there is anything positive to be gleaned from the reports of misconduct, it is that our military leadership in Iraq vigorously pursues reports of wrongdoing and, as far as we know, covers up nothing," says Solis.